There are numerous instances in many areas of technology where it is desirable to fasten a plate, disk, drum or the like to a shaft for rotation with the shaft. There are equally numerous techniques for fastening such items to a shaft, but these techniques are not always satisfactory. In one particular application, shaft encoders marketed by the assignee of the subject invention require that a drum or disk be attached to a motor shaft. The circumference of the drums (or pulse wheels) contain magnetic patterns which are detected by a sensor in a module that is usually affixed to the motor face. The sensor output is used to determine the speed and direction of rotation of the shaft. These drums must be rigidly attached to the shaft either directly or with the aid of an adaptor plate, so that there is no relative motion between the circumference of the disk and the motor shaft. There are many schemes for accomplishing the attachment. Of those available today, many types are able to lock the drum to the shaft sufficiently, but each has drawbacks, some of which are listed below:
costly, precise machining of many parts often required; PA1 time consuming installation due to large number of screws to tighten and other assembly steps; PA1 problematic removal, particularly of wedge type locks; and PA1 high moments of inertia in some devices degrade performance of the device employing the shafts. PA1 Set screws often do not prevent slippage of the adapters in high slew rate applications; PA1 The results are not consistent; PA1 The shafts are deformed when the set screws are tightened. This often makes the adapter difficult to remove. They are often either forcibly pulled off, heated with a torch or simply pounded off with a hammer. This further scores the surface of the shaft which must be smoothed before it can be used again; PA1 Pre-drilled holes are often necessary to get good performance. This is an expensive procedure as the holes must be located accurately. PA1 When the adapter moves with respect to the shaft, the surface of the shaft is further deformed. A valley or gouged out area is left behind the set screws. When the shaft reverses direction, it is far easier for the shaft to follow the valley back to the original position. In high slew rate applications, the valleys get deeper and longer as the directions continue to change. This continuous movement of the adapter is unacceptable. PA1 In some applications, the set screws are small allowing either the set screw threading is stripped or the internal socket structure of the screw is damaged. This prevents further tightening or removing of the screw. PA1 Simple installation, just slide into place and tighten the screw; PA1 Simple removal, just back out the wedge piece; PA1 No shaft indentations or scoring; PA1 No pre-drilling or special shaft preparations; PA1 Very strong attachment; PA1 When a tightened adaptor is moved, there is no deformation of the shaft surface, and the gripping power remains high; PA1 Can use multiple wedges in a single application where extra gripping power is needed; PA1 The adaptor plate does not move when the wedge piece is tightened. This makes alignment easier and installers do not have to determine how far it will move before adaptor is attached firmly; PA1 The taper shaft lock tightens from the front and not the side. Many applications have restrictions that make it difficult to access the side of the plate or disk. PA1 Uses simple tools, i.e., a hex wrench for a standard socket head screw. PA1 a) a wedge shaped piece with a throughbore; PA1 b) a threaded bolt with a first enlarged head passing through the wedge shaped piece; and PA1 c) a radially enlarged collar secured to the threaded bolt downstream from the wedge piece. PA1 a) a rod at least partially threaded at one end; PA1 b) a wedge having a throughbore through which the rod is passed; and PA1 c) a collar on the rod downstream of the wedge piece, the collar fixed to the rod. PA1 a) a threaded bolt having an enlarged head; PA1 b) a wedge piece having a round outer surface interrupted by a tapered flat surface on one side thereof; the wedge piece having a throughbore through which the bolt is passed; and PA1 c) a nut threadably engaged on the threaded bolt downstream of the wedge piece, the nut being bonded to the threaded shank.
Other types of locking devices that are less costly do not lock the drum in place well enough in high slew rate applications. These include use of compression clamping devices such as split C-clamps.
For some applications where a shaft passes through a drum adaptor, set screws have been used to hold the adaptor in place. The set screws are placed on the same longitudinal point on the axis, but separated by 90.degree. about the axis. In this position, each screw pushes the shaft directly against the other side of the adaptor. Because they are transversely located, however, they do not counteract or interfere with each other. Many times a customer will pre-drill holes in the shaft for receiving the set screws that lock the drum in place. In both cases, with and without the pre-drilled holes, the set screws will displace metal when the adaptor rotates relative to the shaft. In fact, there have been numerous field reports of problems with the set screw design, and the complaints include:
There have been many other approaches to firmly attach a disk, drum or plate to a shaft. One of the most common is to use a keyway. For many reasons, however, this is not always appropriate for various applications.
Another approach which produces an excellent grip is often generally referred to as the Ringfedder.RTM. type. Here, a wire is wrapped around the shaft and two disks with a taper on the inner diameter are placed on either side. Bolts are used to clamp the two disks together and, as the tapered internal diameters press against the wire, they are forced against the shaft and the disks. This creates a uniform pressure about the circumference. Although these disks work well, they are too expensive to use. In addition, assembly requires the tightening of many screws which is undesirably time consuming.
Another technique is to use taper bushings which work well but are also expensive. Moreover, removing them is often not an easy task and jacking screws are usually required.
In still another technique, C-shaped rings are placed around the shaft and fingers added to the disk are clamped between the C-clamp and the shaft. Screws are added between the open faces of the C-shaped ring so that when tightened, the clamp traps the fingers and holds the disk to the shaft.
Other methods, such as heat shrinking, are not practical where disks or drums are to be secured to a shaft.